An airport tarmac is just one environment in which windy conditions can adversely affect the serviceability of utility carts. The airport tarmac is a utilitarian surface, used primarily by support personnel in the business of servicing aircraft and transporting baggage. Baggage is some times transported on carts towed behind small motorized vehicles. Other carts are hand-powered. In the case of commuter aircraft, passengers also access the tarmac for boarding the aircraft from the ground. In such cases, it is usual for the airline operator to park a small hand-powered cart between the terminal building and the aircraft.
Passengers place their baggage on this cart as they leave the terminal. Airline personnel may also place the baggage on such a cart for passengers to pick up as they deplane and approach the terminal.
The cart is manually pushed about the tarmac. When placed in the vicinity of aircraft, the cart is subject to aircraft jet blast, propeller wake, and general wind conditions unimpeded by barriers. Baggage carts present a large wind catching surface, particularly when loaded. The above incidents of wind can cause the carts to roll on their wheels, to overpower friction brakes, or to pivot or skid about a non-rotating wheel or wheels. A moving cart is a hazard for personnel, but more frequently becomes a hazard to aircraft. Incidents of an impact of a cart with an aircraft are known and damaging. Contact of a cart is typically between the top or roof of a cart and the highly engineered and easily damaged skin of an aircraft fuselage or with the propeller which can result expensive repair and service costs.
In U.S. Pat. No. 5,862,884 issued to Applicant, the problem of wind has been partially addressed in the implementation of an airfoil on a portable wheelchair lift for use on airport tarmacs. While the use of airfoils on a lift or a cart convert lateral wind loading to a downward force for resisting overturning, it does not address the eventual impact issues with a cart, whether during handling or due to wind.
A variety of prior art carts are in use, none of which have proven particularly satisfactory to the airlines in part because:
they are hard to push; PA1 the carts are insufficiently resistant to being wind driven into the aircraft; or PA1 regardless of the reason for an impact, the contact of a cart and an aircraft results in damage.
It is known to equip prior art carts with brakes, as described in U.S. Pat. No. 3,651,894 to Auriemma. Auriemma discloses a serving cart with friction brakes, operated with a dead-man arrangement of a handle and drum-brakes with an actuating cable therebetween. A spring normally applies braking pressure until the handle is pushed or pulled. In U.S. Pat. Nos. 3,986,582 to Dye and 4,084,663 to Haley, latching type dead-man braking arrangements disclosed for a serving cart and carriage respectively. Both Dye and Haley disclose braking systems which use spring-biased pins which engage complementary opening in the sides of supporting wheels. Dye locates supporting wheels mid-cart and both are fitted with the brakes to avoid rotation.
When the operator releases the brake however, operator inattention can result in a collision with other objects. In the context of an airport tarmac, accidental contact of lower portions of the cart are rarely significant, being with tires or other sturdy structures. However, contact of the top of the cart can happen and is usually with the sensitive aircraft fuselage or a propeller.
No known prior art utility carts employ energy absorbing means about the cart's upper periphery.
Accidental impact has been addressed by others is situation where the damage-sensitive object is moving. In U.S. Pat. No. 2,546,026 to Coon for instance, an early use of a closed coil spring is disclosed as a mounting between an antenna and an automobile. Lateral impact of the antenna causes the spring to deflect, absorbing the energy and avoiding damage to the antenna. In U.S. Pat. No. 5,199,814 to Clark et al., a signpost is fitted with coupling to a base, the coupling permitting the signpost to pivot over from an upright to a prone position when struck by a vehicle. Deflection of the signpost limits damage to the post and to the vehicle. The coupling arrangement utilizes a tension cable between the base and the signpost. Deflection of the signpost and cable compresses a spring within the signpost, allowing the signpost to move and creating a righting force. The top of the post can rotate to the ground if run completely over by the offending vehicle.
In the context of a utility cart used at an airport, the upper structure often serves also as a load-carrying platform. In the case of the prior art coil spring mounting of Coon, the spring is unsuitable for supporting vertical loads, tending to buckle or collapse upon itself. The signpost coupling of Clark et al. has a narrow point of contact which aids in its rotation but does not assist, nor anticipate incorporation of a load-supporting structure while continuing to permit energy-absorbing deflection when struck from the side.
Regarding the braking issue, prior art use of friction brakes is limited to instances where the lateral forces can exceed the frictional pre-load. The extraordinary wind loading imposed on a cart on an airport tarmac can easily overcome friction brakes, particularly if the effectiveness of the brakes depends on wear or maintenance.
Those prior art carts which are fitted with latching type brakes have not dealt with the impact issue which can also occur when an operator has consciously released the brakes.
Therefore, there is a demonstrated need for a utility cart which has a system of supporting wheels and brakes which ensures immobility when stopped and which has an energy absorbing periphery for minimizing or eliminating impact damage regardless of the state of the cart.